From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Djalal Harouni <tixxdz@gmail.com>, Chris Mason <clm@fb.com>,
tytso@mit.edu, Serge Hallyn <serge.hallyn@canonical.com>,
Josh Triplett <josh@joshtriplett.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Andy Lutomirski <luto@kernel.org>,
Seth Forshee <seth.forshee@canonical.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-security-module@vger.kernel.org,
Dongsu Park <dongsu@endocode.com>,
David Herrmann <dh.herrmann@googlemail.com>,
Miklos Szeredi <mszeredi@redhat.com>,
Alban Crequy <alban.crequy@gmail.com>
Subject: Re: [RFC v2 PATCH 0/8] VFS:userns: support portable root filesystems
Date: Tue, 10 May 2016 20:47:40 -0700 [thread overview]
Message-ID: <1462938460.14896.32.camel@HansenPartnership.com> (raw)
In-Reply-To: <20160511005340.GN2694@ZenIV.linux.org.uk>
On Wed, 2016-05-11 at 01:53 +0100, Al Viro wrote:
> On Tue, May 10, 2016 at 04:36:56PM -0700, James Bottomley wrote:
> > +static int shiftfs_rename2(struct inode *olddir, struct dentry
> > *old,
> > + struct inode *newdir, struct dentry
> > *new,
> > + unsigned int flags)
> > +{
> > + struct dentry *rodd = olddir->i_private, *rndd = newdir
> > ->i_private,
> > + *realold = old->d_inode->i_private,
> > + *realnew = new->d_inode->i_private;
> > + struct inode *realolddir = rodd->d_inode, *realnewdir =
> > rndd->d_inode;
> > + const struct inode_operations *iop = realolddir->i_op;
> > + int err;
> > + const struct cred *oldcred, *newcred;
> > +
> > + oldcred = shiftfs_new_creds(&newcred, old->d_sb);
> > + err = iop->rename2(realolddir, realold, realnewdir,
> > realnew, flags);
> > + shiftfs_old_creds(oldcred, &newcred);
>
> ... and you've just violated all locking rules for ->rename2().
Yes, sorry, somehow I missed that when I converted everything else to
the vfs_ functions.
> > +static struct dentry *shiftfs_lookup(struct inode *dir, struct
> > dentry *dentry,
> > + unsigned int flags)
> > +{
> > + struct dentry *real = dir->i_private, *new;
> > + struct inode *reali = real->d_inode, *newi;
> > + const struct cred *oldcred, *newcred;
> > +
> > + /* note: violation of usual fs rules here: dentries are
> > never
> > + * added with d_add. This is because we want no dentry
> > cache
> > + * for shiftfs. All lookups proceed through the dentry
> > cache
> > + * of the underlying filesystem, meaning we always see any
> > + * changes in the underlying */
>
> Bloody wonderful. So
> * we lose caching the negative lookups
We do? They should be cached in the underlying layer's dcache. If
that's not enough, I can hash them, but I was trying to avoid doubling
the dcache size.
> * we've got buggered hardlinks (different inodes for those)
Yes, had a note to do the lookup, but forgot.
> * it has never, ever been tried on -next (would do rather nasty
> things on that d_instantiate())
So this is just a proof of concept; I figured it was best to do it
against current rather than have people who wanted to try it pull in
your tree. I can respin it after the merge window closes.
>
> > +
> > + kfree(sfc);
> > +
> > + return err;
> > +}
>
> > + file->f_op = &sfc->fop;
>
> Lovely - now try that with underlying fs something built modular.
>
> Or try to use it on top of something with non-trivial
> dentry_operations
> (hell, on top of itself, for starters).
So if I add the missing fops_get/put, you're happy with the way this
hijacks f_op and f_inode?
James
next prev parent reply other threads:[~2016-05-11 3:47 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-04 14:26 [RFC v2 PATCH 0/8] VFS:userns: support portable root filesystems Djalal Harouni
2016-05-04 14:26 ` [RFC v2 PATCH 1/8] VFS: add CLONE_MNTNS_SHIFT_UIDGID flag to allow mounts to shift their UIDs/GIDs Djalal Harouni
2016-05-04 14:26 ` [RFC v2 PATCH 2/8] VFS:uidshift: add flags and helpers to shift UIDs and GIDs to virtual view Djalal Harouni
2016-05-04 14:26 ` [RFC v2 PATCH 3/8] fs: Treat foreign mounts as nosuid Djalal Harouni
2016-05-04 23:19 ` Serge Hallyn
2016-05-05 13:05 ` Seth Forshee
2016-05-05 22:40 ` Djalal Harouni
2016-05-04 14:26 ` [RFC v2 PATCH 4/8] VFS:userns: shift UID/GID to virtual view during permission access Djalal Harouni
2016-05-04 14:26 ` [RFC v2 PATCH 5/8] VFS:userns: add helpers to shift UIDs and GIDs into on-disk view Djalal Harouni
2016-05-04 14:26 ` [RFC v2 PATCH 6/8] VFS:userns: shift UID/GID to on-disk view before any write to disk Djalal Harouni
2016-05-04 14:26 ` [RFC v2 PATCH 7/8] ext4: add support for vfs_shift_uids and vfs_shift_gids mount options Djalal Harouni
2016-05-04 14:26 ` [RFC v2 PATCH 8/8] btrfs: " Djalal Harouni
2016-05-04 16:34 ` [RFC v2 PATCH 0/8] VFS:userns: support portable root filesystems Josh Triplett
2016-05-04 21:06 ` James Bottomley
2016-05-05 7:36 ` Djalal Harouni
2016-05-05 11:56 ` James Bottomley
2016-05-05 21:49 ` Djalal Harouni
2016-05-05 22:08 ` James Bottomley
2016-05-10 23:36 ` James Bottomley
2016-05-11 0:38 ` Al Viro
2016-05-11 0:53 ` Al Viro
2016-05-11 3:47 ` James Bottomley [this message]
2016-05-11 16:42 ` Djalal Harouni
2016-05-11 18:33 ` James Bottomley
2016-05-12 19:55 ` Djalal Harouni
2016-05-12 22:24 ` James Bottomley
2016-05-14 9:53 ` Djalal Harouni
2016-05-14 13:46 ` James Bottomley
2016-05-15 2:21 ` Eric W. Biederman
2016-05-15 15:04 ` James Bottomley
2016-05-16 14:12 ` Seth Forshee
2016-05-16 16:42 ` Eric W. Biederman
2016-05-16 18:25 ` Seth Forshee
2016-05-16 19:13 ` James Bottomley
2016-05-17 22:40 ` Eric W. Biederman
2016-05-17 11:42 ` Djalal Harouni
2016-05-17 15:42 ` Djalal Harouni
2016-05-04 23:30 ` Serge Hallyn
2016-05-06 14:38 ` Djalal Harouni
2016-05-09 16:26 ` Serge Hallyn
2016-05-10 10:33 ` Djalal Harouni
2016-05-05 0:23 ` Dave Chinner
2016-05-05 1:44 ` Andy Lutomirski
2016-05-05 2:25 ` Dave Chinner
2016-05-05 3:29 ` Andy Lutomirski
2016-05-05 22:34 ` Djalal Harouni
2016-05-05 22:24 ` Djalal Harouni
2016-05-06 2:50 ` Dave Chinner
2016-05-12 19:47 ` Djalal Harouni
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